In FPD manufacturing devices and semiconductor manufacturing devices, various types of precision chuck or support platform are used to hold a glass substrate or semiconductor wafer. These devices are generally averse to unnecessary reflected or transmitted light.
Japanese Patent Laid-open No. 8-262090 discloses a support platform on which a glass substrate for an LCD (Liquid Crystal Display) is mounted, and which is subjected to alumite processing and blackened. Light is randomly reflected at the surface of the blackened support platform and also absorbed, which means that undesired halation that causes reflection of light is prevented.
Japanese Patent Laid-open No, 8-139168 discloses a vacuum chuck of ceramics formed with a thin film layer of low reflectance. Recently, since it has become possible to provide larger FPD substrates and wafers, there has been an increased demand for ceramics chucks of high specific rigidity (young's modulus/specific gravity). Compared to aluminum, which has a specific rigidity of 28 GPa·cm3/g, Alumina ceramics or AlN ceramics have a specific rigidity of 80–95 GPa·cm3/g or 90–95 GPa·cm3/g.
Japanese Patent Laid-open Nos. 2001-019540 and 10-095673 respectively disclose blackened ceramics with a base of cordierite, and blackened ceramics with a base of AlN. These blackened ceramics are the same insulators as an FPD substrate. If a chuck made of insulating ceramics is brought into contact with an FPD substrate, electrostatic polarization occurs inside the substrate. As a result of this, spark discharge occurs and the substrate is damaged.
Japanese Patent Laid-open No. 11-245133 describes problems caused by electrostatic polarization that occurs, for example, when manufacturing a slider for a magnetic head. A plurality of sliders are obtained by cutting a slider bar having a plurality of thin film elements formed thereon. If the slider bar is joined to an insulating jig, electrical charge is polarized inside the metal layer of the thin film elements. This publication discloses using a jig of semiconductive ceramics in order to solve this problem caused by electrostatic polarization. Surface resistivity of the disclosed jig is within a range of greater than or equal to 1×106 ohms per square to less than 1×1012 ohms per square.
Semiconductor ceramics having a base of alumina (Al2O3) with 0.5–2 wt % TiO2 added is known from Japanese Patent laid-open No. 62-094953. This alumina ceramics is calcinated in a reducing atmosphere.
Japanese Patent laid-open No. 11-189458 discloses semiconductor ceramics having a volume resistivity of 104–1012 Ω·cm, and a withstand voltage of 10 kV/mm or greater. This semiconductor ceramics contains alumina crystal grains of 40–85% by volume, and one or more of MnNb2O6, Mn2AlO4, and MnFe2O4. Comparatively inexpensive alumina is generally calcinated in an ordinary atmosphere, which means that it is possible to manufacture semiconductor ceramics on a large scale.
The object of the present invention is to provide an alumina ceramics having high specific rigidity by including alumina, which is the main component, in a high proportion.
Another object of the present invention is to provide ceramics that satisfies the requirements of low reflectance and semiconductivity, without excessively lowering the proportion of alumina.